1. Field of the Invention
The present invention relates to a direct fuel injection-type spark-ignition internal combustion engine.
2. Description of the Related Art
There has heretofore been known a stratified charge combustion produced by directly injecting fuel into a cylinder to form a mixture (hereinafter referred to as combustible mixture) that can be favorably ignited only in the vicinity of a spark plug, at the ignition timing, to burn a lean mixture in the cylinder as a whole. To carry out the stratified charge combustion, in general, the fuel injection valve injects fuel in the latter half of the compression stroke. It is intended that the thus injected fuel proceeds into a concave combustion chamber formed in the top surface of the piston, is vaporized by robbing heat from the wall surfaces of the combustion chamber, is deflected by the shape of the combustion chamber toward the spark plug, and forms a combustible mixture near the spark plug.
In the direct fuel injection-type spark-ignition internal combustion engine for performing the stratified charge combustion, in general, the spark plug is arranged nearly at the center in the upper part of the cylinder, the fuel injection valve is arranged in the periphery in the upper part of the cylinder, and the combustion chamber extends from nearly the central portion of the top surface of the piston toward the periphery of the top surface of the piston on the side of the fuel injection valve, and includes the bottom wall, the spark plug side wall, and the fuel injection valve side wall. Fuel injected into the combustion chamber collides with the bottom wall of the combustion chamber, thereafter proceeds toward the spark plug side wall along the bottom wall, and thereafter is deflected toward the spark plug by the spark plug side wall.
In order to favorably vaporize the fuel utilizing heat of the wall surface of the combustion chamber, the distance for moving fuel along the wall surface of the combustion chamber must be lengthened so that the injected fuel stays in contact with the wall surface of the combustion chamber for an extended period. In order to realize this without changing the shape of the combustion chamber, it has been proposed to inject fuel at a relatively large acute angle with respect to the horizontal plane. This makes it possible to move the position where fuel collides with the bottom wall away from the spark plug side wall of the combustion chamber, while maintaining the same position of injection hole of the fuel injection valve, as compared with when the fuel is injected at a relatively small acute angle with respect to the horizontal plane, and, hence, to extend the distance the fuel moves on the bottom wall of the combustion chamber.
When the fuel is injected at a relatively large acute angle with respect to the horizontal plane, however, fuel collided with the bottom surface is diverted and all of fuel does not proceed toward the spark plug side wall along the bottom surface; i.e., fuel only partly proceeds toward the fuel injection valve side wall along the bottom surface.
Accordingly, an amount of the combustible mixture formed near the spark plug via the spark plug side wall of the combustion chamber is decreased, and the engine output is not produced as intended. Besides, the mixture formed by fuel proceeding toward the fuel injection valve side wall of the combustion chamber cannot be favorably burned, and unburned fuel may be emitted in increased amounts.